Slashing v2 (probably-not-final)

[cwgoes]

• Evidence queue (kept for one unbonding period relative to discovery) for slashing on unbonding completion, spec updated accordingly Now using eager slashing
• Automatically unbond validators on double-signing
• SlashingKeeper common type in types to expose this functionality for staking
• REST server handler for unrevoke transaction & signing info status queries
• CLI documentation
• Tagged slashing events for UIs

This should be final (for launch). Anything I missed @rigelrozanski? edit: overly optimistic

[rigelrozanski]

We need to update the spec as a part of this ideally - As per our discussion with @sunnya97 - we should now ONLY have eager slashing meaning that we no longer need to maintain the evidence queue. - > as a part of this we don't actually need a slashing keeper in types - because staking complete-unbond transaction no longer needs to perform the slashing

Lastly - let's either open up an issue of implement a "max rebonding/unbonding" slashes per block so if there is a lot to iterate through it happens over multiple blocks

[cwgoes]

Ref #1348

[cwgoes]

Ref #1378

[cwgoes]

Ref #1440

This is probably not final slashing at this point, but the next revision should come after a more clearly-defined security model.